1. Field of the Invention
This invention relates to a method of manufacturing a liquid crystal display device, and in particular to a method of scanning a linear energy beam for crystallizing amorphous silicon into polycrystalline silicon by irradiating the linear energy beam onto the amorphous silicon plural times.
2. Description of the Related Art
As a method of manufacturing a thin film transistor of a liquid crystal display device, there has been developed a method of forming source and drain regions, which is featured in that part of amorphous silicon layer is converted to a low resistance layer by partially polycrystallizing the amorphous silicon layer. As a method of polycrystallizing an amorphous silicon layer, an energy beam is employed to melt and then recrystallize the amorphous silicon layer.
As for the method of irradiating the energy beam, there is proposed in Japanese Patent Unexamined Publication Shou/61-187,222 a method of linearly irradiating the energy beam.
Further, Japanese Patent Unexamined Publication Hei/2-78,217 discloses a method of irradiating a linear energy beam by scanning it plural times in such a manner that an overlapping region is constantly formed between the neighboring irradiated regions of the energy beam.
However, if an overlapping region of energy beam is constantly formed as mentioned above, the irradiation dosage of the energy beam at the overlapping region naturally becomes larger than that in other regions, so that the characteristics of a thin film transistor, in particular, the threshold characteristics thereof is delicately altered, thereby giving rise to a problem of non-uniformity of display image. In particular, if the irradiation of energy beam is carried out so as to constantly form an overlapping region as mentioned above, the non-uniformity of display image is caused to appear in the form of a straight line and in a visually exaggerated manner.